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The Male Reproductive System

Find out more about the anatomy, functions, and disorders of the male reproductive system.

The male reproductive system is designed to produce and distribute sperm and the male hormone testosterone. The pituitary gland begins to secrete hormones that stimulate the male's testicles to produce testosterone. Testosterone causes sperm production and male puberty. Once male puberty has taken place, the male reproductive system will produce millions of sperm cells every day. The parts of the male reproductive system include the testicles (or testes) (1), the penis (2), the duct system (the epididymis and vas deferens) (3), the accessory glands (seminal vesicles and prostate) (4), and the scrotum (5). The testicles lie outside the body inside a protective sac called the scrotum. The epididymis and the vas deferens are the duct system for transporting sperm. The accessory glands include the seminal vesicles and the prostate gland. Their job is to lubricate the system and nourish the sperm. The reproductive function of the penis is to distribute sperm into the vagina.

Illustrations by Catherine Delphia.

The Testicles

The two testicles (1), or testes, are oval-shaped glands about 1 inch wide and 2 inches long. Because they produce sperm best at a temperature slightly lower than body temperature, they hang outside the body in their scrotal sac (2). If it gets too cold, the scrotum will shrink and draw them up closer to the body. The testicles are constantly producing and storing testosterone and millions of sperm cells.

Duct System: The Epididymis and Vas Deferens

The epididymis (1) is a network of coiled tubes that sit alongside the testicles. Sperm (2) move out from the testicles into the epididymis to complete their development. During the four to six weeks it takes a sperm cell to make its way through these tubes, the sperm become mature. A mature sperm looks like a tiny fish with a head (this part contains its genes) and a tail that allows it to swim toward the egg. The vas deferens is also called the sperm duct. These ducts carry the sperm from the epididymis to the prostate gland (3).

Accessory Glands: The Seminal Vesicle and Prostate

There are several glands that help produce semen, or seminal fluid. The seminal vesicle (1), located behind the bladder (2), produces the whitish fluid, or the semen, needed for the sperm to reach the intended egg. Each sperm is only 1/600 of an inch long and can live inside the female reproductive system for up to 48 hours. The prostate gland (3) makes a fluid that helps the sperm move more quickly through the female reproductive system.

The Penis

The penis is an essential component of male sexual anatomy. It’s made up of two parts: the shaft (1) and the head (2) (also called the glans penis). The small slit at the glans tip is the opening of the urethra, which is the tube that carries semen into the vagina. Urine also passes through the urethra (3), but not during sexual functioning. The glans is normally covered by a fold of skin called the foreskin. Removal of the foreskin is called circumcision. Though not medically necessary, circumcision is often done for cultural, religious, or hygienic reasons.

Erection and Erectile Dysfunction

When a man becomes sexually aroused, the penis becomes harder and longer – this is called an erection. The penis is made up of a spongy tissue (1) filled with nerves and blood vessels, which allows it to be stimulated and to fill with blood, causing an erection. On average, an erect penis (2) can increase in length to 5 to 6 inches and circumference to 4 to 5 inches. When the erect penis is stimulated, ejaculation can occur. In an average ejaculation there may be up to a teaspoon of fluid containing up to 500 million sperm. The inability to have or maintain an erection is called erectile dysfunction, or ED; it's also sometimes referred to as impotence. The risk for this condition increases with age, but is not a normal part of aging. ED may be due to emotional or physical factors. Common conditions that may contribute to ED include diabetes, depression, obesity, and smoking.

Infections of the Male Reproductive System

Infections can enter the male reproductive system through the opening of the urethra and spread to the glands, ducts, or testicles. Many types of infections can be sexually transmitted, including gonorrhea, chlamydia, genital herpes, genital warts (1), human papillomavirus (HPV), and HIV/AIDS, and syphilis. Germs that cause sexually transmitted infections include bacteria, viruses, and parasites. Symptoms of an infection may include pain when passing urine or on ejaculation and discharge from the urethra. Untreated infections can damage the male reproductive system and possibly result in infertility. Correctly using a latex condom can reduce the risk of many of these infections.

Disorders of the Testicles

Because of their position outside the body, the testicles can be easily injured. A testicle can also become twisted and cut off its own blood supply. This is an emergency situation that may require surgery. If a testicle changes in shape or size, it could be a sign of testicular cancer. This type of cancer usually occurs between the ages of 15 and 40 and is very treatable when discovered early. The prostate gland (1) is another source of possible problems in the male anatomy. Enlargement of the prostate (2) is common in men over the age of 50. This enlargement, called benign prostatic hypertrophy, or BPH, often causes urinary obstruction and urinary frequency. Prostate cancer of the prostate gland is the most common cancer in men; if discovered early, it’s quite treatable.

Male Infertility

Male infertility problems are the cause of roughly one-third of all infertility cases — and there are often no warning signs. Blockage in any part of the reproductive system that delivers sperm, such as the epididymis or vas deferens, can cause infertility. Some other common causes of male infertility include varicoceles, low sperm count, abnormally shaped sperm (1), undescended testicles, STDs, and medical problems like kidney failure. Some cases of infertility have no known cause and can even be genetic.

Vasectomy

According to the National Center for Health Statistics, approximately 6 percent of couples in the United States cite vasectomy as their method of contraception. The only form of permanent birth control currently available to men, vasectomy has become a simple operation done under local anesthetic. The conventional vasectomy technique involves making two incisions near the scrotum to remove a portion of the vas deferens (1). Now, there’s also a no-scalpel vasectomy in which a surgeon locates the vas deferens under the skin and then cuts and ties it (2) through a small incision. The reversal of a vasectomy is quite difficult.